The use of a fluid pressure signal, particularly when in the form of a vacuum signal, has traditionally been a primary means of controlling various functions associated with internal combustion engines such as ignition timing, emission control, fuel flow and the like. Generally, the fluid pressure signal is provided by regulation of a fluid pressure regulator that is provided with fluid pressure (commonly a vacuum) from a source powered by the engine. Typically the regulated fluid pressure signal is provided by the movement of some type of valve associated with the regulator such that the movement thereof regulates the fluid pressure supplied to the regulator to provide the fluid pressure output signal.
Generally, it has been of interest in the past to monitor engine operating conditions such as changes in mass air flow through the engine or changes in the engine's coolant fluid temperature by some type of mechanism that is able to move a regulator valve to provide a regulated fluid pressure signal for accomplishing some desired function. An example of the use of a fluid pressure regulator that utilizes changes in temperature for providing a vacuum control signal for controlling the temperature of an automotive air conditioning system is disclosed in U.S. Pat. No. 3,770,195 and a barometric sensing fluid pressure regulator covering mechanisms for converting changes in barometric pressure into a fluid pressure control signal for controlling various emission control devices and engine operating parameters is disclosed in my copending United States patent application Ser. No. 309,286. An example of a governor in combination with an electromechanical device for use in a cruise control system for controlling the speed of an engine above a predetermined speed is disclosed in U.S. Pat. No. 3,298,482.
Although the previously described mechanisms have been individually used to advantage in the past to control various devices associated with internal combustion engines, particularly of the type used in motor vehicles, no one had thought up until the time of the present invention that changes in the rotational speed of the engine could be simply and effectively utilized to maintain a desired engine idling speed nor that the desired idling speed of the engine could be effectively maintained by use of a fluid pressure signal singularly or in combination with one or more fluid pressure signals that are proportional to changes in operating conditions of the engine other than its rotational speed such as, for example by the integrator mechanism for combining two or more fluid pressure signals to provide a single output fluid pressure signal disclosed in my copending United States patent application Ser. No. 289,545.